1. Field of the Invention
The present invention relates to methods for producing a piezoelectric actuator and a liquid discharge head based on the use of the aerosol deposition method.
2. Description of the Related Art
A certain kind of ink-jet head, which is provided for an ink-jet printer, includes a piezoelectric actuator and a flow passage unit in which nozzle openings and ink flow passages communicating with the nozzle openings are formed. The piezoelectric actuator has a vibration plate which covers openings of pressure chambers formed in the ink flow passages of the flow passage unit. A lower electrode, a piezoelectric layer, and an upper electrode are stacked on the vibration plate. When the electric field is applied between the lower electrode and the upper electrode, the vibration plate is flexibly bent or warped in accordance with the deformation of the piezoelectric layer. The ink contained in the pressure chamber is pressurized, and the ink is discharged from the nozzle opening.
An annealing treatment is applied to the stack of the vibration plate and the piezoelectric layer in the steps of producing the piezoelectric actuator as described above in order that the piezoelectric characteristic, which is required to sufficiently warp the vibration plate, is given to the piezoelectric layer. However, when the annealing treatment is performed at a high temperature exceeding 600° C., then any element contained in the vibration plate is diffused into the piezoelectric layer, and the piezoelectric characteristic of the piezoelectric layer is deteriorated in some cases. A vibration plate made of stainless steel is often used for the piezoelectric actuator, because stainless steel is cheap and excellent in the processability. However, since stainless steel contains metal elements such as Fe and Cr which are easily diffused into the piezoelectric layer, the diffusion of the elements contained in the vibration plate into the piezoelectric layer is especially conspicuous. In view of the above, a piezoelectric actuator is provided, which is provided with a layer of an insulating oxide such as alumina as a diffusion-preventive layer between the vibration plate and the piezoelectric layer.
In the piezoelectric actuator, grooves are sometimes formed at positions of the vibration plate corresponding to the spaces between the pressure chambers in order that the pressure chambers, which are arranged closely and adjacently, are prevented from any interference, and the vibration plate is warped to such an extent that the liquid droplets can be jetted even when a relatively low voltage is applied. As a method for producing such a piezoelectric actuator, Japanese Patent Application Laid-open No. 2006-96034 discloses that a diffusion-preventive layer is formed by using the aerosol deposition method (hereinafter referred to as “AD method”) on a vibration plate previously formed with grooves, and a piezoelectric layer is further formed on the diffusion-preventive layer by using the AD method.
In this context, the AD method is such a film formation method that a film containing a component of material particles is formed on a film formation surface by jetting a preparation (aerosol) obtained by dispersing the material particles in a gas toward the film formation surface, and making the material particles collide with the film formation surface so that the material particles are deposited thereon. In general, a film-forming apparatus for carrying out the AD method includes a pressure-reducing vessel, an aerosol generator, and a jetting nozzle connected to the aerosol generator. The film formation objective is arranged movably in the horizontal direction on the ceiling of the pressure-reducing vessel. The jetting nozzle is arranged under or below the film formation objective so that the jetting direction thereof is substantially perpendicular to the film formation objective surface of the film formation objective. The relative position of the film formation surface is changed with respect to the jetting nozzle by moving the film formation objective substantially in the horizontal direction while fixing the jetting nozzle, and thus the aerosol is blown toward a wide range of the film formation objective surface.
As described in Japanese Patent Application Laid-open No. 2006-96034 as well, the AD method can be used in order to form the diffusion-preventive layer on the vibration plate in the steps of producing the piezoelectric actuator. However, the angle, which is formed by the film formation objective surface of the film formation objective and the jetting direction of the jetting nozzle, is maintained to be substantially constant in the film-forming apparatus for carrying out the AD method. Therefore, the dead angle or dead area, against which the aerosol jetted from the jetting nozzle does not abut, appears on the inner wall of the groove depending on the shape of the groove provided on the vibration plate. A portion appears, in which the thickness of the diffusion-preventive layer is extremely small. In such a situation, if the annealing treatment is applied to the stack of the vibration plate, the diffusion-preventive layer, and the piezoelectric layer, then the elements of the vibration plate are diffused into the piezoelectric layer from the portion at which the thickness of the diffusion-preventive layer is insufficient, and the piezoelectric characteristic of the piezoelectric layer is deteriorated.